The present invention relates to the texturing of magnetic data storage media, and more particularly to the texturing of dedicated transducing head contact zones (also called landing zones) of such media to reduce friction and improve wear, while also minimizing system resonance.
Laser textured magnetic disks, particularly those textured over areas designed for contact with data transducing heads, are known to reduce friction and improve wear characteristics as compared to mechanically textured disks. Traditional laser texturing involves focusing a laser beam onto a disk substrate surface at multiple locations, forming at each location a depression surrounded by a raised rim as disclosed in U.S. Pat. No. 5,062,021 (Ranjan) and U.S. Pat. No. 5,108,781 (Ranjan). An alternative, as disclosed in International Publications No. WO 97/07931 and No. WO 97/43079, is to use a laser beam to form domes or nodules, rather than rims. In some cases, each of the domes is surrounded by a raised rim. The features can have either circular or elliptical profiles.
Collectively, the texturing features form a texture pattern or distribution throughout the head contact zone. A particularly preferred pattern is a spiral, formed by rotating the disk at a controlled angular speed while moving a laser radially with respect to the disk. The laser is pulsed to form the individual texturing features. For example, the disk can be rotated to provide a circumferential speed of about one meter per second. Then, operating the laser at 50,000 pulses per second provides a 20 micron circumferential pitch, i.e. distance between adjacent texturing features. The radial speed of the laser controls the radial pitch or spacing between adjacent turns of the spiral, which also can be about 20 microns.
Although this approach has been highly successful in terms of reducing dynamic friction and improving the wear characteristics of dedicated transducing head contact zones, the regular, repeating pattern of the laser texture features produces strong input excitations based on the fundamental frequency of the circumferential pitch, including higher order harmonics. When the excitation frequencies coincide with natural frequencies of the slider or its gimbal and support system, resonance occurs which results in a high amplitude acoustic energy signal, which can increase the difficulty of determining the glide avalanche breaking point (a disk/transducing head spacing value) and yield a false indication that the disk has failed a glide test.
Several previously proposed media texturing alternatives address these difficulties to a degree. For example, the aforementioned International Publication Number WO 97/43079 includes the observation that mechanically textured disks, as compared to laser textured disks, produce less acoustic energy during head take-off and landing. A noise-reducing texturing alternative is discussed therein; namely, rows of rims connected to one another at their ends, as shown in FIG. 15 of the publication. In International Application Serial No. PCT/US98/05283 entitled xe2x80x9cLow Resonance Texturing of Magnetic Media,xe2x80x9d filed Mar. 13, 1998, resonance-reducing texturing is disclosed in the form of elongate circumferential ridges, most notably a continuous ridge in the shape of a spiral throughout the transducing head contact region. Although these alternatives afford considerable reduction in noise during head take-off and landing, there remains a need for noise-reducing texturing arrangements compatible with substantial spacing between adjacent texturing features. These arrangements frequently are preferred due to lower manufacturing costs and better potential for producing a uniform roughness throughout the head contact zone.
According to another alternative approach, the contact zone is textured with an irregular sequence of spaced-apart texturing features forming a substantially circumferential, spiral path. Multiple turns of the spiral path define a uniform radial pitch. By contrast, the circumferential pitch is irregular, determined according to a pseudo random function in which the actual spacing intervals vary about a nominal interval, over a range comparable to but generally less than the nominal interval. This approach is disclosed in International Application Serial No. PCT/US98/05340 entitled xe2x80x9cMagnetic Media with Randomly Positioned Texturing Features,xe2x80x9d filed Mar. 18, 1998. While this approach has been found quite useful in minimizing resonance effects, the manufacturing advantages afforded by texture patterns of constant radial and circumferential pitch underline the desire for texturing approaches that minimize resonance effects without the need for random spacing intervals. More particularly, randomizing circumferential pitch involves additional control equipment, e.g., a random signal generator or means to accelerate and decelerate a rotating substrate disk. Also, care must be taken to assure that a texture pattern, although randomized, has a substantially constant average feature density across a slider contact area.
Therefore, it is an object of the present invention to provide a substrate texturing process in which resonance effects are minimized without randomizing the spacing between adjacent texturing features, in particular without randomizing circumferential pitch within an annular contact zone.
Another object is to provide a substrate for a magnetic data recording medium, in which multiple texturing features formed within a contact zone of the substrate are specially shaped to reduce resonance effects.
A further object is to provide a process for forming multiple texturing features on the substrate surface of a substrate for a data recording medium, in which the texturing features exhibit fast roll-off profiles, more particularly bell-shaped profiles that more effectively diminish higher order harmonics excitation.
Yet another object is to provide a data recording medium with a dedicated transducer contact zone textured to minimize the occurrence of false failure episodes during glide avalanche testing.
To achieve these and other objects, there is provided a substrate for a magnetic data storage medium of the type including a data zone for storing data and a contact zone textured for a contact with a data transducing head maintained apart from the data zone by an air bearing during use of the data storage medium. The substrate includes a substrate body having a substantially planar substrate surface including a data zone and a contact zone. The substrate body is adapted for movement substantially parallel to the substrate surface in a predetermined direction with respect to a data transducing head. Multiple texturing features are formed in the contact zone, and are projected outwardly from the substrate surface. Each of the texturing features has bell-shaped profiles taken in planes substantially perpendicular to the substrate surface and oriented in the predetermined direction. The texturing features further have diameters, taken in the predetermined direction, of at least about three microns.
As used in this application, the term xe2x80x9cbell-shaped profilexe2x80x9d refers primarily to the smoothness of the profile, and to the nature of its changing slope. In particular, for a texturing feature projected upwardly from a horizontal surface, the slope is zero (representing a horizontal segment) at the point of maximum texturing feature height. The profile curves in both directions away from the maximum height point, in both cases with the slope smoothly increasing, until a maximum slope is reached along a medial region between the horizontal surface and the height of the texturing feature. Then, on both sides the curve continues its downward course, but with a smoothly decreasing slope, thus to create at the bottom of the profile an outward flare.
Preferably the maximum height point is at the center of the profile, with the profile being symmetrical about the maximum height point. In fact, most preferably each profile represents a Gaussian curve, i.e., a normal curve, with the maximum height at the center, corresponding to the mean in the usual Gaussian curve, and with a standard deviation "sgr" corresponding to at least 0.5 microns, so that the 6"sgr" span that encompasses over 99.7% of the area beneath the curve corresponds to a diameter of at least three microns.
The texturing features can be formed with uniform heights and diameters. Preferably, uniform heights are within the range of 5-30 nm, and diameters are in the range of 3-5 microns.
Although the bell-shaped profiles are of particular importance in the predetermined direction of travel relative to transducing heads, the texturing features also can exhibit bell-shaped profiles in planes perpendicular to the substrate surface, and substantially perpendicular to or at inclined angles with respect to the predetermined direction.
A surprising and beneficial result of the multiple bell-shaped texturing features is the rapid decay of the higher order harmonics of fundamental excitation frequencies. This considerably diminishes the likelihood of resonance effects due to frequencies arising due to circumferential pitch interacting with natural frequencies of the PZT slider or its gimbal and support system. Accordingly, glide avalanche testing is much less likely to yield false indications of failure, even when the texture pattern has a constant circumferential pitch.
Another aspect of the present invention is a process for selectively texturing a recording medium substrate, including the following steps:
a. providing a substrate body having a substantially planar substrate surface; and
b. within a selected zone of the substrate surface, forming multiple texturing features, each texturing feature having a bell-shaped profile taken in planes substantially perpendicular to the substrate surface and in a predetermined direction of travel of the substrate body relative to a data transducing head when a data recording medium incorporating the substrate body is used in conjunction with the data transducing head to perform data operations.
Preferably the texturing features are formed by directing a pulsed coherent energy beam toward the substrate body and causing the coherent energy beam to impinge upon the substrate surface at a plurality of selected locations thereon, altering the topography of the substrate surface at each selected location to form one of the texturing features. An area of impingement of the coherent energy beam on the substrate surface has a diameter of at least three microns.
This is the presently preferred texturing method, and involves a departure from the prevailing tendency in the art favoring smaller laser texturing features, e.g., with diameters of at most 1 micron. To form the larger-diameter texturing features, the laser energy beam is maintained at approximately the same power level, but is not focused to the extent previously deemed appropriate, so that the area of impingement on the substrate surface has the desired size of at least three microns rather than a diameter of 1 micron or less.
Further, it has been found that texturing features formed on aluminum nickel-phosphorus substrates tend to assume crater or sombrero shapes, more particularly with a rounded rim above the substrate surface encircling a depression. Thus, it has been found useful to apply a glass layer to an Al Nixe2x80x94P substrate before texturing. A glass substrate, on the other hand, can be laser textured directly.
Other techniques are contemplated for forming the desired texture. For example, multiple texturing features can be formed simultaneously by a pressing or stamping operation, in lieu of laser texturing. An etching process also may be used, although present etching techniques are not expected to yield features with the desired smoothness in their curvature, and thus are less preferred.
Thus in accordance with the present invention, the texturing features throughout a contact zone are shaped to exhibit profiles that resemble Gaussian curves, especially in the direction of travel of the data storage medium relative to data transducing heads. A rapid decay of higher order harmonics of the fundamental frequencies arising from a constant pitch of the texturing features, considerably diminishes the chances of resonance effects based on such frequencies and the natural frequencies of the head and its gimbal and support system. This is particularly advantageous during glide avalanche testing, because the reduced occurrence of resonance effects leads to correspondingly reduced false failure indications.